1. Field of the Invention
The subject invention generally relates to pre-combustion apparatus for reducing emissions in internal combustion engines, and is specifically directed to a self-contained pre-combustion chamber adapted to be field retrofitted in an internal combustion engine.
2. Description of the Prior Art
The use of a pre-chamber in an engine cylinder head is well known. As early as 1876, an Otto engine included an explosion canal in the cylinder head to improve ignition and enhance combustion. The explosion canal was designed to draw in a rich mixture at the very end of the intake stroke, whereby that portion of the charge was exposed to the igniter flame, creating a strong jet of flame which blasted into the combustion chamber for ensuring a quick, positive burning of the total charge. Pre-chamber technology was routinely utilized in high speed racing engines of the 1920's. Cooper-Bessemer incorporated a jet cell in 1938 to achieve charge stratification in the combustion chamber.
The original application of the pre-chamber in gas engines was in the Fairbanks-Morse two-cycle opposed piston engine, used extensively in the electric power generation industry. While the initial interest in pre-combustion chamber technology was to permit use of alternative fuels or to even out the operation of inefficient engines at low speed and low load, this technology has current value because of the emission reduction resulting from the use of pre-combustion systems, even in today's more efficient engines. With the enactment of the Clean Air Act of 1977, conventional engines could no longer meet the emission requirements.
Recently, a number of designs have been tried to improve the emission rating of such engines. One such design is the Cooper CleanBurn design which employs a jet cell igniter installed in the conventional head in place in one of the spark plug wells. The jet cell igniter incorporates a small pre-chamber into which a conventional spark plug is installed and an additional supply of fuel is introduced through a check valve. The timing of the auxiliary fuel supply into the cylinder is accomplished by the differential pressure existing across the check valve. When pressure in the main cylinder and pre-chamber is lower than the fuel supply pressure to the igniter, the check valve will open and fuel will flow into the pre-chamber. When the main chamber and pre-chamber pressure rises to a level higher than the auxiliary fuel supply pressure the check valve will close and block the flow of auxiliary fuel. More recently, pre-chambers have been incorporated in both four-cycle and two-cycle engines in order to reduce emission levels. While very successful in achieving lower emissions, the cost factor in upgrading to engines including pre-chambers in prohibitive. While many engines are "grandfathered" in, it is becoming more and more difficult to meet emission requirements without use of a pre-chamber.
It is now possible to retro-fit older engines by placing the pre-chamber in one spark plug well. While such applications are successful in reducing emissions, the life span of the pre-combustion chamber assembly is substantially less than that of the engine, per se. This is primarily due to the rapid heat change within the pre-combustion chamber, resulting in stress cracking and accelerated fatiguing of the assembly. Therefore, there remains a need for a longer life pre-combustion chamber assembly which can be retrofit on existing engines.